1. Field of the Invention
This invention relates to a rotary transformer used in a rotary magnetic head unit having a magnetic head such as that used in, for example, a VTR so as to transmit a signal between a rotary part and a stationary part of the VTR without any physical contact between these parts.
2. Description of the Prior Art
A rotary core and a stationary core having a frequency characteristics most suitable or optimum for a signal to be transmitted for recording and reproduction (which signal will be referred to hereinafter as a record/reproduce signal) and made of a ferrimagnetic material such as a ferrite are disposed opposite to each other while defining a very small gap of about several ten microns between them. Coil grooves are formed on the confronting surfaces of the rotary core and the stationary core respectively. A coil of an electrically conductive material having one to several turns is disposed in the coil groove of the rotary core, and the ends of this coil are connected to a magnetic head which acts to record/reproduce the signal. Similarly, a coil of an electrically conductive material having its number of turns determined according to a predetermined step-up ratio with respect to the coil of the rotary core is disposed in the coil groove of the stationary core, and the ends of this coil are connected to a circuit, etc. mounted on the stationary part.
It is the recent trend that an spparatus such as a high-vision TV set or a digital VTR that can record a signal having a very high frequency becomes more and more popular. Therefore, in order to minimize a signal transmission loss which is undesirable, it is a common practice to mount a signal amplifier on the rotary part in the vicinity of the magnetic head so as to amplify the signal reproduced by the magnetic head. As a result, electric power is required for driving the signal amplifier.
Heretofore, a contact type method using a slip ring and a brush has been used to supply required electric power from the stationary part to the rotary part. However, the slip ring and the brush contacting each other generates pulse-shaped low-frequency noise called brushing noise that adversely affects the picture quality. Also, the slip ring and the brush are subjected to heavy wear. Further, with the increase in the rotation speed, the phenomena described above tend to become more and more marked. Therefore, another rotary transformer of a non-physical contact type is recently used for the purpose of electric power signal transmission too. That is, a rotary transformer having its frequency response different from that of the record/reproduce signal transmission purpose rotary transformer is located at a specific position different from the position of the latter rotary transformer.
The operation of the rotary transformers constructed as described above will now be described.
In the signal record mode, a recording signal is supplied to the coil of the stationary core of the record/reproduce signal transmission purpose rotary transformer, so that a magnetic flux path is formed between the stationary core and the rotary core. As a result, a voltage is induced in the coil of the rotary core due to mutual induction, and the signal is transmitted from the stationary core to the rotary core not physically contacting the stationary core.
In the signal playback mode, a reproduced signal induced by the magnetic head is supplied to the coil of the rotary core in a relation contrary to the record mode, and a voltage is induced in the coil of the stationary core by mutual induction too, so that the signal is transmitted from the rotary .part to the stationary part without any physical contact between them. Further, in order to supply electric power to the signal amplifier on the rotary part from the stationary part by the electric power signal transmission purpose rotary transformer, this electric power signal is converted into a direct current by a direct current converter mounted similarly on the rotary part and drives the signal amplifier.
However, the prior art construction has had various problems as will be pointed out now.
(1). The record/reproduce signal transmission purpose rotary transformer and the electric power signal transmission purpose rotary transformer must be separately provided. Therefore, connecting members which are twice as many as those used hitherto will be required so that coils led from the cores are to be connected to the circuit, etc. Thus, the overall construction will not meet the requirement for the size reduction, and the degree of freedom of the system design will be quite lowered. Also, the cost will be inevitably increased.
(2). When the record/reproduce signal having a high frequency and a low signal level and the electric power signal having a low frequency and a high signal level are transmitted by the use of the same kind of cores, the frequency characteristics of the cores is necessarily limited to a certain predetermined value, and those signals having substantially the same frequency range can only be efficiently transmitted. Therefore, even when it is desired to use the same kind of cores for the transmission of a plurality of signals having extremely different frequency ranges, such as, the record/reproduce signal and the electric power signal, it becomes difficult to efficiently transmit one of these signals because the frequency characteristics of the cores are not optimized to deal with both of these signals.